This invention relates to transducers for ink jet systems and, more particularly, to a new and improved ink jet transducer arrangement.
In U.S. Pat. No. 4,584,590, a shear mode transducer for an ink jet system is described in which a piezoelectric transducer plate is polarized in the direction perpendicular to the plane of the plate and is positioned in an ink jet head so as to provide one wall of a series of adjacent pressure chambers. By applying an electric field between adjacent electrodes mounted on one surface of the transducer at locations between the center of an ink jet pressure chamber and the periphery of the pressure chamber, the transducer may be actuated in the shear mode so that the chamber wall is deflected inwardly into the chamber to apply a pressure pulse to the ink within the chamber and thereby eject a drop of ink from the ink jet orifice communicating with the pressure chamber.
This transducer arrangement is advantageous in that the piezoelectric transducer may be polarized in the same direction and uniformly over its entire area, permitting the use of convenient transducer polarization techniques. The amount of shear motion produced by a piezoelectric transducer subjected to an electric field orthogonal to the direction of polarization in this arrangement is controlled by the d.sub.15 coefficient, which is typically about 0.5 nanometer per volt. As a result, a relatively high voltage difference must be applied to the electrodes, which are mounted at relatively small spacings on the transducer, to obtain the required transducer deflection. For example, as described in the above-mentioned U.S. Pat. No. 4,584,590, a potential of about 200 volts is applied to electrodes which are spaced by about 0.02 inch. Accordingly, extreme care must be exercised with such transducers to make certain that there are no short circuits or leakage paths between the electrodes and substantial insulation must be maintained on the conductors leading to the transducer. These precautions add to the complexity and weight of an ink jet head which is mounted for high-speed reciprocating motion on a carriage in normal ink jet operation.